Interpretation of Geohazards Related to Offshore Salt Karst

Abstract

Summary Several authors have identified salt karst as a geohazard onshore and offshore. I study how the expression of different salt karst features can be interpreted to assess geohazards related to salt tectonics. In the Green Canyon area of the USA Gulf of Mexico, three different mechanisms generating salt karst are identified for breaking the caprock, providing access for low-salt-saturation seawater dissolving the salt and causing collapse of the caprock. Active diapirism exciting extensional stress on the caprock, collision of salt diapirs with gravity gliding of salt canopy exciting compressional stress on the caprock, and differential gravity gliding of different sections of the salt canopy resulted in shear stress of the caprock. These three mechanisms have been identified as the primary sources for offshore salt karsting. Erosion by strong deep-water currents, which has previously been considered a significant cause of salt karsting, appears to be a secondary process contributing to the overall efficiency of the salt dissolution. This approach allows mapping geohazards such as unstable caprock as well as delineating lineaments that are interpreted as strike-slip faults in the seafloor and that cannot be detected otherwise because strike-slip faults do not show any vertical offset of the seismically detectable strata.